Effusive FIP in cats: how long antiviral treatment lasts
9-month-old Ragdoll with abdominal effusive FIP and no neurological or ocular signs. He has been on oral GS-441524 for 3 weeks: the fever resolved within days, the ascites has gone, he eats well and has gained weight. The owners ask whether they can stop treatment now.
What is the most appropriate recommendation?
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A. Stop it now, because clinical remission means the cat is cured
Clinical improvement comes long before viral clearance. Stopping the antiviral after a few weeks risks relapse, often with neurological or ocular involvement, which is harder to treat.
B. Replace the antiviral with prednisolone as maintenance treatment
Glucocorticoids have no effect on the virus and do not prevent relapse. Before antivirals they only gave temporary relief; they are not maintenance treatment for FIP.
C. Complete about 12 weeks (84 days), recalculating the dose as weight changes, and stop when clinical signs and bloods (haematocrit, globulins, albumin:globulin ratio) have normalised
Correct. The reference course is 84 days. Cats gain weight during treatment, so the dose must be adjusted at every check to avoid underdosing. It is stopped once the cat is asymptomatic with normalised bloods, and monitoring continues afterwards.
D. Continue it lifelong at a low dose to prevent relapse
There is no basis for indefinite treatment, and low doses favour resistance and relapse. A full course at an effective dose is given, followed by monitoring.
lightbulb Key takeaway
Check the cat every 4 weeks: weight (with dose adjustment), haematocrit, total protein, globulins and albumin:globulin ratio. Some studies have had good results with shorter courses, but 84 days remains the reference. Relapses usually appear in the weeks or months after stopping.
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Updated: October 31, 2026 · Educational content for veterinary professionals. It does not replace current clinical guidelines or the judgement of the attending veterinarian.